When an aqueous solution of sodium molybdate is added to an aqueous solution of ferric chloride, acidified with acetic acid, a giant {Mo72Fe30} cluster is instantaneously formed as the amorphous substance Na-2[Mo72Fe30O252(CH3COO)(4)(OH)(16)-(H2O)(108)]center dot 180 H2O (1). Compound 1 consists of aggregated nanovesicles of {Mo72Fe30} clusters, as confirmed by field-emission scanning electron microscopy and transmission electron microscopy images of 1. An aqueous suspension of 1 upon moderate heating results in the formation of crystalline nanoferric molybdate, which gives insight into understanding the formation of a yellow coating mineral, ferrimolybdite, frequently found on the ores of molybdenum.